1. Field of the Invention
The present invention relates to a method for determining an amount of exposure, and particularly to a method for determining an amount of exposure in which when color copy or black-and-white copy of a color original image is effected, data of a human image which is a main image including a human face is extracted from the color original image, and an amount of exposure is determined on the basis of the extracted data.
2. Description of the Related Art
When a photograph of a person is viewed, the region which is most noticed is the person's face. In order to produce a photograph of high quality, it is necessary to print the person's face at a proper color and a proper density.
Conventionally, there has been known a method in which a human face region in an original image of a color film is designated by a light pen, density data of the human face is extracted, and on the basis of the extracted density data, an amount of exposure is determined so that the color and density of the face can be printed appropriately. The technique like the above is disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 62-115430, 62-115431, 62-115432, 62-189456, 62-189457, 63-138340, and 63-178222.
However, in the above-described prior art, since it is necessary that an operator should designate the face region by the light pen for each of images, a drawback arises in that a lot of time is required for a printing operation. Further, since the operator must visually designate the face region, automation of the operation is difficult.
Further, there has been known a method in which a magnetic layer is formed on a reverse surface of a color film, magnetic information including camera information about a type or the like of camera, photographing information such as a focal length at the time of photographing processing, f-number, and the like, development information such as a number for indicating a processing laboratory, and the like is recorded, and an amount of exposure is determined by using the magnetic information. The technique like this is disclosed in U.S. Pat. Nos. 5,130,745 and 5,194,892.
However, even if the magnetic information is recorded on the color film as described above, it is not possible to designate a main subject on the color film. For this reason, the operator must designate the face region in a visual manner.
Accordingly, there has been proposed a method for automatically extracting data of a human face. As an example of this method, a method for extracting data of a human face by extracting flesh-color data is disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 52-156624, 52-156625, 53-12330, 53-145620, 53-145621 and 53-145622. Namely, a color original image is divided into a large number of photometric points, each of the photometric points is separated into three colors of R (red), G (green) and B (blue) and is photometrically measured, and then, it is determined whether the color of each photometric point calculated from the obtained photometric data exists in a flesh-color range. A cluster (group) of photometric points which has been judged to be in the flesh-color range is set as face density data.
However, in this method, the color in the flesh-color range is assumed to be the face density data. For this reason, the density data of flesh-colored or approximately flesh-colored regions other than the face region, for example, ground or tree trunks, which exist as a background of a main subject, or clothes of a person may be mistakenly extracted as the face density data. Accordingly, the face density data extracted in accordance with photographic scenes differ from each other, and there is a possibility that only the face density data cannot be automatically extracted in a stabilized manner. For this reason, there exists a drawback in that color and density of a printed to be prepared cannot be reproduced appropriately.
In order to solve this drawback, there has been proposed a method for extracting data of a human face from a histogram for the hue or the saturation, which is disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 4-346332 and 4-346334. Namely, a histogram for the hue or the saturation is obtained on the basis of data obtained by photometrically measuring light into which three colors are separated, a color original image is divided by a hue value or a saturation value corresponding to each population, a region representing the feature of an image is selected from the divided regions, and data of the selected region is extracted as feature image data, namely, human face data.
However, it is very likely that a region near an edge which is separated from a central portion on a color original image will be a background, and there is a low possibility that an image corresponding to a main subject (which is principally an image of a human face and will be hereinafter referred to as a human image) is included in this region. Accordingly, in the case in which the feature image data is extracted from the histogram for the hue or the saturation in the above-described manner, if a region similar to the human face exists in the background, data of the background is also extracted in addition to the human image data. As a result, the color and density of a print to be prepared becomes unstable.
Consequently, there has been proposed a method for extracting data of a human face from an effective region with a background having a low probability of including a human image which is eliminated from a color original image. An example of this method is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 6-186652, in which region merging is carried out in such a manner that pixels are merged by using data obtained by photometrically measuring light into which three colors are separated and a region whose size is largely different from that of a main subject, which is obtained based on photographing information such as a focal length or the like recorded on a color film, is judged to be a background region and excluded from the merged regions. The density of the human image is estimated from the effective region after the background has been excluded and the estimated density is set as the human density data.
However, even in the effective region from which the background is excluded, it is difficult to automatically specify a position of a human image included in this effective region. For this reason, when an amount of exposure is determined by using the extracted data, the color and density of a print to be prepared becomes unstable.